1. Field of the Invention
The subject invention relates to the novel method for the densification of glass-forming materials including, for example, sand, limestone and fluxes, such as soda ash and the like. Moreover, the subject invention particularly relates to the formation of glass-producing materials by compacting the materials into discrete bodies that are shock resistant within a short period of time for subsequent transfer to a glass-producing operation.
2. Description of the Prior Art
In the conventional manufacture of glass, loose glass-forming materials are introduced into a glass-producing furnace, generally in a dry or, if desired, moistened condition. In such operations materials are mixed prior to introduction into the furnace by any of a number of mixing means well-known to the art. Although the glass-forming materials are well mixed, it is generally found that subsequent processing and handling of the mixed loose batch materials often causes segregation. Thus, because of the different densities and particle size of the materials, there is a marked tendency of the various ingredients to settle or separate one from the other. This segregation of the loose glass batch material is objectionable in that nonuniform charges of ingredients are introduced into the furnace. Moreover, in such methods of conveying loose batch materials, there is formation of dust that, to say the least, causes a nuisance in the immediate working area. Further, when introduced into the furnace, the dust associated with the loose batch materials influences melting of the refractory surfaces and clogging of the checkers, as well as flues of the furnace system.
In the past, the problem of dust carry-over and segregation of constituents has been particularly troublesome where very fine particle sizes make up a substantial portion of the batch material. It has been proposed to form discrete units via compacting or agglomerating, wherein the glass batch materials may include binders to cement together the various constituents. In practice, this has been done by simply admixing with the glass batch mixture a suitable binder, such as calcium oxide, sodium hydroxide or sodium silicate in small amounts, and mechanically forming the mixture into the desired discrete units, for example, by molding the mass while in its moldable state, in conventional briquetting machines.
Aside from segregation and dusting problems, it has been found advantageous to compact glass batch materials for other reasons. As relatively inexpensive sources of fuels have come to an end, means for conserving or substantially reducing energy to melt glass batch materials has been extensively investigated. It is known that the melting of raw glass materials to form a typical soda-lime glass is theoretically possible, for example, at about 1600.degree. F., but due to the relatively small surface contact areas between the particles in loose glass batch this theoretical value is not realized. In practice, temperatures in the range of about 2700.degree. F., to 2800.degree. F., are required to homogenize glass at rates necessary to meet demands of high volume production. It is known that by increasing the amount of surface contact between particles via compaction lower temperatures of melting can be approached. By using conventional compacting techniques, such as briquetting, the density of the glass batch materials can be easily increased within a range of about 1.90 to about 2.20 gms/cm.sup.3. Since the volume of voids are substantially reduced over dry, loose batch materials, and the contact of particles greater, the ease of melting is significantly enhanced.
Although conventional compacting methods have been employed in the past, it has been found that the compact units so formed, such as briquettes, lack the necessary shock resistance and strength for further processing, especially shortly after their formation. In this regard, the compact units are especially susceptible to breakage or fracture right after their compaction resulting in spillage of their powdery ingredients and fragments. Such breakage is objectionable not only in spillage of materials but also in presenting subsequent processing difficulties, especially where heat transfer and prereaction are contemplated. In these situations it is advantageous that the compact units be uniform in size and that their integrity be maintained with minimum breakage prior to their ultimate introduction into a glass-producing furnace.
U.S. Pat. No. 2,366,473 to Bair relates to forming pebble-like units without special binders by using fluxes, sand with fines and water. Soda ash is disclosed as producing a chemical setting that effectively bonds particles of material together. U.S. Pat. No. 3,065,090 to Hopkins relates to a method of mixing soda ash solutions and sand to produce a wet mixture to form agglomerates. U.S. Pat. No. 3,081,180 to Krinov discloses tumbling a wet mixture of salts and sand to form agglomerates and feeding the same into a glass furnace while at a temperature of between 90.degree. F., and 200.degree. F., to prevent setting of said mixture so as to maintain it in a wet state. U.S. Pat. No. 4,023,976 to Bauer, et al., discloses a briquetting process for glass-producing furnaces wherein glass batch materials are compacted with a binder and are subsequently divided into particulate form prior to briquetting.